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Cycle 23 STIS Instrument Handbook
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Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 23 > Chapter 9: Overheads and Orbit-Time Determination > 9.2 STIS Exposure Overheads

9.2
Our current estimates of the overheads on STIS exposures are summarized in Table 9.1 and Table 9.2. All numbers given are approximate and rounded up to the nearest half minute; they do not differentiate in detail the overheads for different STIS modes and configurations. These overhead times are to be used (in conjunction with the actual exposure times and the HST Primer) to estimate the total number of orbits for your proposal. After your HST proposal is accepted, you will be asked to submit a Phase II proposal to support scheduling of your approved observations. At that time you will be presented with actual, up-to-date overheads by the scheduling software. Allowing sufficient time for overheads in your Phase I proposal is important; additional time to cover unplanned overheads will not be granted later.
The following list presents important points for each type of overhead:
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For V 21 point sources, 6 minutes.
For diffuse acqs, add 0.2 checkbox2 seconds to the nominal 6 minutes.
For V 21, 6 minutes for one peakup; note that a second peakup is required for the 0.1X0.03 aperture; dispersed light peakups may require an additional 3 minutes overhead for change in optical element.
More generally, see Table 8.5, Peakup Scan Sequences and Parameters for Supported Spectroscopic Slits.
 
5.01
8.02
1.03
5.04
8.05
1
Includes auto wavecal. At Phase II, wavecals occurring at the beginning or end of an orbit will be pushed into occultation, providing increased time for scientific observing.
2
Includes auto wavecal. At Phase II, wavecals occurring at the beginning or end of an orbit will be pushed into occultation, providing increased time for scientific observing.
3
For CR-SPLIT=n, each exposure has a 1 minute overhead, so there will be (n – 1) minutes of extra overhead. If small CCD subarrays are used, the overhead per exposure decreases to 20 seconds.
4
Includes auto wavecal. At Phase II, wavecals occurring at the beginning or end of an orbit will be pushed into occultation, providing increased time for scientific observing.
5
Includes auto wavecal. At Phase II, wavecals occurring at the beginning or end of an orbit will be pushed into occultation, providing increased time for scientific observing.
6
Use these only for additional wavecal exposures beyond those taken automatically.


Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 23 > Chapter 9: Overheads and Orbit-Time Determination > 9.2 STIS Exposure Overheads

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